NAPLEX Examination.
Practice Question # 26.
Naplex
Topiramate (Topamax) NAPLEX Review
Mechanism of action.
Topiramate is a derivative of fructose. It decreases rapid hippocampal neuronal fi ring, possibly because of sodium- or calcium-channel inhibition. It is also a weak carbonic anhydrase inhibitor and a sodium-channel blocking agent. Topiramate potentiates the activity of GABA. It has been shown to be eff ective adjunctive therapy for partial seizure treatment in adults, tonic–clonic seizure, infantile spasms, and Lennox–Gastaut syndrome.
Administration and dosage
- Adults 17 years and older, 25 to 50 mg/day, up to 400 mg/day in two divided doses. Children 2 to 16 years, 1 to 3 mg/kg/day, up to 5 to 9 mg/kg/day in two divided doses.
- Topiramate is 80% bioavailable, and food does not aff ect its bioavailability.
- Dose adjustment is necessary for patients with renal or hepatic impairments.
- Enzyme-inducing anticonvulsive drugs can decrease topiramate levels, but topiramate has a signifi cant eff ect on metabolism of other anticonvulsive drugs.
- Initial treatment is 50 mg daily, followed by titration to an eff ective dosage. More than 400 mg daily has not been shown to improve response.
Precaution and monitoring effects
- Increased incidence of kidney stones (renal calculus) in older patients who received this drug. Patients should be advised to increase intake of fl uids while taking topiramate.
- Paresthesia is a common side eff ect of anhydrase inhibitors.
- Due to eff ect of topiramate, renal bicarbonate loss and metabolic acidosis could occur.
- Topiramate could cause oligohidrosis and hyperthermia (decrease sweating and increase temperature).
- Acute myopia with secondary angle closure glaucoma could occur, typically occur within 1 month of therapy in which the drug should be discontinued.
(6) Adverse effects
- Th e physician should be notifi ed if any of the following adverse eff ects occur:
- Breast pain in females
- Nausea or tremor, which are dose-related side eff ects.
- Back pain, chest pain, dyspepsia, or leg pain
